Adding sum and average extensions

[kamaal111]

This PR adds new array extension methods for calculating sums and averages of array elements using key paths. It introduces support for both numeric types that conform to AdditiveArithmetic and provides specialized handling for floating-point and integer types.

Key changes:

• Added sum(by:) method that calculates sums using key paths for any AdditiveArithmetic type
• Added average(of:) methods with overloads for BinaryFloatingPoint and BinaryInteger types
• Added comprehensive test coverage for the new functionality including edge cases like empty arrays

[Copilot]

Pull Request Overview

This PR adds new array extension methods for calculating sums and averages of array elements using key paths. It introduces support for both numeric types that conform to AdditiveArithmetic and provides specialized handling for floating-point and integer types.

Key changes:

• Added sum(by:) method that calculates sums using key paths for any AdditiveArithmetic type
• Added average(of:) methods with overloads for BinaryFloatingPoint and BinaryInteger types
• Added comprehensive test coverage for the new functionality including edge cases like empty arrays

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
Sources/KamaalExtensions/Array.swift	Implements sum and average extension methods with comprehensive documentation
Tests/KamaalExtensionsTests/ArrayTests.swift	Adds extensive test coverage for new sum and average methods, plus formatting improvements to existing tests

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[Copilot]

The magic number 21.3333333333 should be calculated as 64.0/3.0 to make the expected result clearer and more maintainable.

Suggested change

	#expect(abs(avgAge - 21.3333333333) < 0.000001)
	#expect(abs(avgAge - (64.0 / 3.0)) < 0.000001)